While the functions of REM sleep remains to be determined, there are a few promising theories which, when taken together, suggest that REM sleep may serve several functions. This research is designed to provide a coordinated body of evidence which are relevant to the validity of one of these theories, i.e., the theory which states that REM sleep plays a role in activating and sustaining behavior. This theory was formulated to help explain the long lasting remissions that Vogel produced in the behavior of severely endogenously depressed patients follow exposure to REM sleep deprivation. For the most part, studies that are relevant to the validity of this theory have been designed to test the effects of one acute period of exposure to REM deprivation on immediate changes in the behavior of rats. While it is true that the results of these studies indicate that REM sleep deprivation has an activating effect on some behaviors, it is not known, if the effects persist. Thus, this research was designed to provide first-time evidence on the longer-term effects of exposure to REM sleep deprivation. By using a standardized methodology and empirically determined observation periods, collectively the six studies proposed here, should provide data that reflect critically on the claim that REM sleep deprivation has immediate and persistent effects on the motivation behavior.